This invention relates to a process for preparing certain catalytically active metal complexes. More particularly this invention relates to such a process involving oxidation of the metal center of a complex to form active catalyst compositions useful for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers.
The use of homogeneous Ziegler-Natta type catalysts in the polymerization of addition polymerizable monomers is, of courser well known in the prior art. In general, these soluble systems comprise a Group 4 or Lanthanide metal compound and a metal alkyl cocatalyst, particularly an aluminum alkyl cocatalyst. Several preparations for homogeneous olefin polymerization catalysts are known. These involve reacting a transition metal chloride with an aluminum alkyl, reacting a transition metal alkyl and a aluminum alkyl, reacting a transition metal alkyl with a proton source, or reacting a transition metal alkyl with a cationic oxidant. In these examples the oxidation state of the transition metal remains unchanged or may actually be reduced.
In Polyhedron, 8(13-14), 1838-1843 (1989), M. Bochmann et al., disclosed an oxidative process for preparing bispentamethylcyclopentadienyltitanium methyl tetraphenylborate using silver tetraphenylborate oxidant in tetrahydrofuran solvent. The complex was inactive in the polymerization of ethylene.
In J. Am. Ch. Soc. 109, 4111-4113 (1987) there is disclosed a process for preparation of cationic zirconium (IV) benzyl complexes by one electron molecular oxidation of d.sup.O organometallic compounds in tetrahydrofuran or methylene chloride solvent.
In application Ser. No. 07/642,111, filed Jan. 16, 1991, a metal center oxidation and cation forming process employing a cationic oxidizer is disclosed. In pending application Ser. No. 545,403, filed Jul. 3, 1990, there are disclosed certain novel constrained geometry complexes possessing unique catalytic properties. In pending application Ser. No. 547,718, filed Jul. 3, 1990 there is disclosed a unique molecular oxidative activation procedure for preparing complexes useful as addition polymerization catalysts. For the disclosures contained therein the preceding United States patents and pending applications are hereby incorporated by reference in their entireties.
The present invention lies in the discovery of a novel technique for preparing certain metal complexes involving both metal center oxidation and cation complex formation via electron transfer in a single step by use of a neutral organic oxidant. Beneficially, the use of neutral reactants permits the synthesis to be performed in hydrocarbon solvents normally employed for olefin polymerizations instead of polar or oxygenated solvents. Consequently, in the present invention contamination with deactivating substances is reduced and the need to substitute solvents prior to use of the resulting complexes is omitted, thereby simplifying the synthesis and use of the complexes as catalysts.
In one embodiment of the invention, the reduced remnant of the oxidizing agent comprises an anion able to ligate the metal complex. To counteract this ligating effect of the resulting residual organic anion, a Lewis acid mitigator is additionally added to the reaction mixture. Thus the process is adaptable for use even where the byproducts may interfere with the desired metal complex formation.
According to the present invention there is provided a process for the preparation of a cationic metal complex corresponding to the formula: EQU [Cp.sub.a (ZY).sub.b ML.sub.c.sup.+ ].sub.q [J.sub.p A].sup.-q,
Wherein:
Cp independently each occurrence is a cyclopentadienyl group q-bound to M, or a hydrocarbyl, silyl, halo, halohydrocarbyl, hydrocarbylmetalloid or halohydrocarbylmetalloid substituted derivative of said cyclopentadienyl group, said Cp containing up to 50 nonhydrogen atoms, and, when a is 2, optionally both Cp groups may be joined together by a bridging group; PA1 a is 1 or 2; PA1 b is 0 or 1; PA1 c is 1 or 2; PA1 the sum of a, b and c is 3; PA1 Y is a linking group comprising nitrogen, phosphorus, oxygen or sulfur covalently bonded to M and Z through said nitrogen, phosphorus, oxygen or sulfur atom; PA1 L independently each occurrence is hydride, halo, or a monovalent anionic ligand selected from covalently bonded hydrocarbyl, silyl, amido, phosphido, alkoxy, aryloxy, and sulfido groups optionally being further substituted with one or more amine, phosphine, ether, or thioether groups, said ligand having up to 50 nonhydrogen atoms, PA1 M is titanium or zirconium in the +4 oxidation state; PA1 p is an integer from 0 to 4; PA1 q is 1 or2; PA1 J is the Lewis acid mitigating agent, and PA1 A is a reduced remnant of a neutral organic oxidizing agent and may be ligating or nonligating, PA1 the steps of the process comprising contacting under conditions to form the oxidized metal complex: PA1 1) a reduced metal precursor complex corresponding to the formula: Cp.sub.a (ZY).sub.b M* L.sub.c, wherein Cp, Z, Y, L, a, b, and c are as previously defined, and PA1 M* is the same metal as M but in a +3 oxidation state; PA1 2) a neutral organic oxidizing agent, A*, capable of accepting one or more electrons and oxidizing M* to M and which in reduced form is A; PA1 and, if A is a ligating group, PA1 a Lewis acid mitigating agent, J.
Z is a divalent moiety comprising oxygen, nitrogen, phosphorous, boron, or a member of Group 14 of the Periodic Table of the Elements, said moiety having up to 30 nonhydrogen atoms;